It is common for the menstrual cycles to be irregular up to the age of 18 years in some people. Since you are 21, the cause of your irregular cycles must first be elicited. If you are sexually active, then you need to get a pregnancy
also excluded. Excessive estrogen
in the body can lead to nausea
, weight gain and amenorrhea
, i.e., absence of period. Pain in lower abdomen soon after eating and frequent urge to urinate is likely due to some infection. I suggest that you see a doctor to get a complete checkup and advice. Take care.